Method of fabricating a miniature device having an acoustic diaphragm

ABSTRACT

A method of forming a device having a compliant member includes providing an elastomeric layer in an uncured state. The elastomeric layer is pre-cured to increase its viscosity. Subsequently, a bobbin and housing, each having an end, can be positioned such that their ends extend at least partially into the elastomeric layer. The elastomeric layer is cured to secure it to the bobbin housing. Examples of pre-cure and cure operations include one or more of a thermal cure, evaporative cure and ultraviolet cure, and the application of moisture, microwave energy and chemical additive. Due to the increased viscosity after the pre-cure, the migration of elastomeric material is substantially reduced relative to an uncured elastomeric material. The reduction in elastomeric material migration results in smaller menisci formed along the walls of the housing and bobbin, and reduced thinning of the compliant member formed at their ends.

BACKGROUND

This disclosure relates to a miniature device having a compliant member.More particularly, the disclosure relates to a method of fabricating anacoustic diaphragm on the miniature device.

SUMMARY

In one aspect, a method of fabricating a device having a complaintmember includes providing an elastomeric layer in an uncured state. Theelastomeric layer is pre-cured to increase a viscosity of theelastomeric layer. One or more of a bobbin and a housing, each having anend, are positioned such that the end of the one or more of a bobbin anda housing extends at least partially into the elastomeric layer. Theelastomeric layer is cured such that the elastomeric layer is secured tothe one or more of the bobbin and the housing.

Examples may include one or more of the following features:

The pre-curing may include applying heat to the elastomeric layer toincrease a temperature of the elastomeric layer to a first temperatureand the curing of the elastomeric layer may include applying heat to theelastomeric layer to increase the temperature of the elastomeric layerto a second temperature that is greater than the first temperature. Thepre-curing may occur for a first duration and the curing may occur for asecond duration, wherein the first duration is less than the secondduration.

The pre-curing may include irradiating the elastomeric layer withultraviolet light for a first duration and the curing may includeirradiating the elastomeric layer with ultraviolet light for a secondduration, wherein the second duration is greater than the firstduration.

The pre-curing of the elastomeric layer may include irradiating theelastomeric layer with ultraviolet light at a first irradiance and thecuring of the elastomeric layer comprises irradiating the elastomericlayer with ultraviolet light at a second irradiance, wherein the secondirradiance is greater than the first irradiance.

The pre-curing may include applying heat to the elastomeric layer andirradiating the elastomeric layer with ultraviolet light. The curing mayinclude applying heat to the elastomeric layer and irradiating theelastomeric layer with ultraviolet light.

The elastomeric layer may be secured to the bobbin and the housing, andthe method may further include removing a portion of the elastomericlayer that extends outside a diameter of the housing.

The elastomeric layer in an uncured state may include liquid siliconerubber.

The positioning of the one or more of a bobbin and a housing may furtherinclude positioning the bobbin inside the housing.

In accordance with another aspect, a device includes a compliant memberand one or more of a bobbin and a housing. The compliant member has asubstantially planar shape and is formed of a single layer of a curedelastomeric material. Each of the one or more of a bobbin and a housinghas an end that extends at least partially into the compliant member.The elastomeric material adheres to a portion of the housing and/orbobbin at the end of the housing and/or bobbin to form a meniscus havinga height defined along a wall of the housing and/or bobbin. The heightof the meniscus is less than a height of a meniscus formed along thewall of the housing and/or bobbin for an uncured state of theelastomeric material.

Examples may include one or more of the following features:

The housing may be a tube having an opening at the end. The elastomericmaterial may include a silicone rubber.

The compliant member may include a meniscus formed at each of an innerwall surface of the housing and/or bobbin and an outer wall surface ofthe housing and/or bobbin.

In accordance with another aspect, a microspeaker device includes anacoustic diaphragm, a housing, a bobbin and a coil. The acousticdiaphragm has a substantially planar shape and formed of a single layerof a cured elastomeric material. The housing has an end extending atleast partially into the single layer. The single layer adheres to aportion of the housing at the end of the housing to form a firstmeniscus having a height defined along a wall of the housing. The heightof the first meniscus is less than a height of a meniscus along the wallof the housing for an uncured state of the elastomeric material. Thebobbin is disposed inside the housing and has a surface and an endextending at least partially into the single layer. The single layeradheres to a portion of the bobbin at the end of the bobbin to form asecond meniscus having a height defined along a wall of the bobbin. Theheight of the second meniscus is less than a height of a meniscus alongthe wall of the bobbin for the uncured single layer of the elastomericmaterial. The coil is wound on the surface of the bobbin.

Examples may include one or more of the following:

The housing and the bobbin may be formed of different materials.

The height of the first meniscus may be different from the height of thesecond meniscus.

The first meniscus may include a first inner meniscus having a heightalong an inner wall surface of the housing and a first outer meniscushaving a height along an outer wall surface of the housing and thesecond meniscus may include a second inner meniscus having a heightalong an inner wall surface of the bobbin and a second outer meniscushaving a height along an outer wall surface of the bobbin.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of examples of the present inventiveconcepts may be better understood by referring to the followingdescription in conjunction with the accompanying drawings, in which likenumerals indicate like structural elements and features in variousfigures. The drawings are not necessarily to scale, emphasis insteadbeing placed upon illustrating the principles of features andimplementations.

FIG. 1A, FIG. 1B and FIG. 1C are a perspective illustration, aperspective cutaway illustration and an exploded cutaway illustration,respectively, of an example of a microspeaker for a miniature earbud.

FIG. 2 is a flowchart representation of an example of a method offorming a device having a compliant member.

FIG. 3A, FIG. 3B and FIG. 3C are cross-sectional illustrations showingsequentially how the method of FIG. 2 is applied to fabricate amicrospeaker device.

FIG. 4 is a magnified view of a portion of the end of the microspeakerdevice of FIG. 3C showing menisci formed at the housing and bobbinwalls.

FIG. 5 is a flowchart representation of an example of a method that usesa thermal pre-cure and cure to form a device having a compliant member.

FIG. 6 is a graphical depiction of a relationship between viscosity andtemperature for an elastomeric material that is suitable for a heatcure.

FIG. 7 is a flowchart representation of an example of a method that usesan ultraviolet irradiation pre-cure and cure to form a device having acompliant member.

FIG. 8 is a graphical depiction of viscosity as a function of bothirradiance and duration of UV exposure for a UV-curable elastomericmaterial.

DETAILED DESCRIPTION

Modern in-ear headphones, or earbuds, typically include microspeakers.The microspeaker may include a coil that is attached to an acousticdiaphragm either directly or through a bobbin on which the coil iswound. Motion of the diaphragm due to an electrical signal provided tothe coil results in generation of an acoustic signal that is responsiveto the electrical signal. The microspeaker typically includes a housing,such as a sleeve or tube, which encloses the bobbin, coil and a magneticstructure. As the size of the earbud decreases, it becomes increasinglydifficult to fabricate the acoustic diaphragm with an elastic suspensionat one end of the bobbin (or coil) and housing.

FIG. 1A, FIG. 1B and FIG. 1C are a perspective illustration, aperspective cutaway illustration and an exploded cutaway illustration,respectively, of an example of a microspeaker 10 that can be used in aminiature earbud. The microspeaker 10 includes a cylindrical housing 12having an opening at both ends. Inside the housing 12 is a bobbin 14that is nominally cylindrical in shape and which is open at least at oneend. The housing 12 and bobbin 14 are secured at one of their ends to acompliant member 16. In some examples, the housing 12 is made ofstainless steel and the bobbin 14 is made of a polyimide (e.g., KAPTON®)or polyethylene terephthalate (PET) (e.g.,)MYLAR®. A magnet assembly 18is secured to a platform 19 at an end of the housing 12 that is oppositeto the compliant member 16. The magnet assembly 18 includes two magnetpieces 18A and 18B separated by a coin 18C. The magnet assembly 18extends along an axis 20 of the housing 12 and into an open regioninside the bobbin 14. In one example, the magnet pieces 18A and 18B arecylindrical neodymium magnets. A coil 22 is wound onto an outsidesurface of the bobbin 14. The bobbin 14 moves substantially along thehousing axis 20 in response to an electrical current conducted throughthe coil 22. In turn, a central circular portion of the compliant member16 moves axially and displaces air to thereby create an acoustic signal.

One technique for fabricating the compliant member 16 includes placingan open end of the housing 12 and an open end of the bobbin 14 into asingle thin layer of liquid silicone rubber. The liquid silicone rubberis then cured to form the compliant member 16. The central region of thecompliant member 16 that is located within the end region of the bobbincan be stiffened while the annular region that surrounds the centralregion remains compliant. Difficulties arise with this technique as theliquid silicone has a surface tension that causes the liquid to adhereto and “climb up” the walls of the housing 12 and the bobbin 14 to forma meniscus. The migration of the liquid silicone to the walls can occurquickly, for example, within a few seconds of placing the ends of thehousing 12 and bobbin into the liquid silicone rubber. The result of themigration is a reduction in the thickness of the layer of silicone whichcan lead to holes in the compliant member 16. Holes can form during thedemolding process because the compliant member 16 is weakened at thethinned areas. In addition, thinned areas may result in tearing or holesbeing formed in the compliant member 16 during operation of themicrospeaker 10.

FIG. 2 is a flowchart representation of an example of a method 100 offabricating a device having a compliant member. Reference is also madeto FIGS. 3A to 3C which are cross-sectional side view illustrationsshowing, in a sequential manner, the method 100 as applied tofabrication of a microspeaker device in which the compliant member cansubsequently be processed to form an acoustic diaphragm and a surround.

According to the method 100, an elastomeric layer 22 is provided (110)in an uncured state as shown in FIG. 3A. The elastomeric layer 22 may bea thermoset rubber such as a silicone rubber or a polyurethane which canbe subsequently cured, for example, by the application of heat (thermalcuring), air (evaporation curing), moisture, microwave energy,ultraviolet (UV) radiation and/or chemical additive. The elastomericlayer 22 is provided on a release liner 24 that is removed at a latertime during the fabrication process. The viscosity of the siliconegenerally is sufficient such that the thickness of the applied layerdoes not significantly change although surface features and bumpstypically disappear over time until the surface is substantially flat.By way of specific non-limiting examples, the silicone rubber may be anELASTOSIL® 3070 Series self-adhesive liquid silicone rubber availablefrom Wacker Chemie AG of Munich, Germany, the polyurethane may beMPP-W43C polyurethane gel or GK-22 polyurethane gel, both available fromNorthstar Polymers, LLC of Minneapolis, Minnesota, and the liner 24 maybe a 40 μm thick LOPAREX® 5100 Series fluorosilicone release lineravailable from LOPAREX LLC of Cary, N.C. The thickness of the uncuredelastomeric layer 22 may vary according to particular applicationrequirements. By way of a specific non-limiting example, the thicknessof the uncured elastomeric layer 22 may be in a range from about 50 μmto about 100 μm.

The elastomeric layer 22 is pre-cured (120) to increase its viscosity.As used herein, “pre-cure” means increasing the viscosity of theelastomeric material so that it is more viscous that theoriginally-provided elastomeric material and less viscous than theelastomeric material in a fully-cured state. The material is partiallycured to attain a viscosity at or just below the gel point, which isdefined as the crossover point of the storage modulus and loss modulus.Above this viscosity, the material exhibits elastic-like behavior andpotting the components into the elastomer is no longer possible. Thus apre-cured material is more resistant to flow than the uncured materialwhile a material that has been cured (i.e., is fully-cured) is generallyin a toughened or hardened state and is not subject to flow. Theviscosity of the elastomeric material generally increases withincreasing cure fraction although the change in viscosity with curefraction is not necessarily linear.

Subsequent to the pre-cure, a housing 28 and bobbin 30 (only endportions illustrated) are positioned (130) such that their ends extendat least partially into the elastomeric layer 22 as shown in FIG. 3B. Inone example, the housing 28 is in the form of a hollow cylindrical tubeand the bobbin 30 is configured to move in a bi-directional manner alongthe tube axis. The housing 28 and bobbin 30 may be positioned at thesame time. Alternatively, the housing 28 and bobbin 30 may be positionedat different times as long as the viscosity of the elastomeric materialdoes not significantly change between the times of positioning of thetwo items. Due to the increased viscosity after the pre-cure, themigration of the elastomeric material is substantially reduced relativeto what would otherwise occur for the uncured elastomeric material. Thereduction in elastomeric material migration results in smaller menisciformed along the walls of the housing 28 and bobbin 30 as describedfurther below.

The elastomeric material is cured (140) so that the ends of the housing28 and bobbin are secured to the elastomeric layer 22. The release liner24 is then removed so that the elastomeric layer 24 remains as asubstantially planar compliant member that adheres to the end of thehousing 28 and the bobbin 30. The central region of the compliantmember, (i.e., the area defined within the diameter of the bobbin 30)can be stiffened to form the acoustic diaphragm. The annular areasurrounding the central region defines a compliant surround that cansupport the bobbin 30 and coil, and enables the acoustic diaphragm tomoves axially to thereby generate an acoustic signal. The portion of thecompliant member that extends beyond the outer diameter of the housing28 may be removed by any of a variety of techniques such as by trimmingor using a punch tool.

FIG. 4 shows a magnified cross-sectional view of a portion of the endsof the housing 28 and bobbin 30 corresponding to the left side of FIG.3C. A meniscus 32 is formed at locations where the elastomeric materialhas climbed (vertical migration in the figure) the walls of the housing28 and bobbin 30. Thus there is an inner meniscus 32A and an outermeniscus 32B along an inner wall surface 34 and an outer wall surface36, respectively, of the housing 28. Similarly, there is an innermeniscus 32C and an outer meniscus 32D along an inner wall surface 38and an outer wall surface 40, respectively, of the bobbin 30. Eachmeniscus 32 has a height H₁ defined from the top surface 42 of theelastomeric layer 22. The menisci 32 are formed during a period of timestarting when the ends of the housing 28 and bobbin 30 are firstpositioned in the pre-cured elastomeric layer 22. All menisci 32 areshown as having the same height H₁; however, the heights along the twowalls may differ due to a difference in material migration along thewalls according to differences in the wall materials.

FIG. 4 shows that the bottom of the walls are not coincident with thebottom of the elastomeric layer 22 as there is some affinity between theelastomeric material and the wall regardless of the pre-cure viscosity.The distance from the bottom of the walls to the bottom of the layer 22is affected by the viscosity increase achieved during pre-cure.

Due to the increased viscosity of the pre-cured elastomeric layer 22 andthe corresponding reduction in material migration, the height H₁ of themenisci 32 is substantially less than a height H₂ of the menisci thatotherwise would have formed using an uncured elastomeric layer. As aresult, less thinning occurs and there is a substantial reduction inthickness variations across the elastomeric layer 22. Advantageously,the fabricated device is easier to remove from the release liner (notshown) without tearing or generating holes. Moreover, the opportunityfor holes or tears to be generated during operation of a microspeakerdevice fabricated with the compliant member is reduced or eliminated. Anadditional advantage is a more consistent stiffness of the suspensiondefined by the peripheral portion of the compliant member that surroundsthe inner acoustic diaphragm. It should be noted that the elimination ofthe menisci 32 is not a goal as they represent an increased area ofadherence to the walls of the housing 28 and bobbin 30, and tearing canoccur when the release liner is removed if no menisci are present. Inaddition, the menisci 32 limit the stress concentration at the jointbetween the elastomer and the housing and bobbin walls.

Reference is made to FIG. 5 which shows a flowchart representation of anexample of a method 200 of fabricating a device having a compliantmember in which the fabrication utilizes a thermal pre-cure and thermalcure. An elastomeric layer is provided (210) in an uncured state and thetemperature of the layer is increased (220) to increase the viscosity ofthe elastomeric material to an intermediate level (i.e., a level that isless than the viscosity for a full cure). Reference is also made to FIG.6 which shows a relationship between viscosity and temperature for anexample of a silicone elastomer that is suitable for a heat cure. Belowa temperature T₁, the viscosity decreases slightly with increasingtemperature. Between the temperature T₁ and a greater temperature T₂,the viscosity increases rapidly with temperature. The viscosity maychange by a factor of approximately 100 or more between temperatures T₁and T₂. At temperatures greater than T₂, the viscosity increasesgradually with increasing temperature.

For a thermal pre-cure, heat is applied to the elastomeric layer toincrease its temperature to greater than temperature T₁ but well belowtemperature T₂. By way of a non-limiting example, the pre-curetemperature of the elastomeric layer may be in a range from about 35° C.to about 100° C. Point 44 indicates one example of a pre-cure operatingtemperature. The result of the pre-cure operation is a sufficientincrease in viscosity such that the elastomeric material is moreresistant to flow and to the formation large menisci while stillallowing the ends of the housing and bobbin to be placed properly in theelastomeric layer. For example, the elastomeric layer on a release linermay be passed through a process line oven, or by one or more heaterlamps or elements, to achieve the desired temperature. By way ofexample, the duration in which the elastomeric layer is at the pre-curetemperature may be less than a minute to more than ten minutes. It willbe appreciated that the selected temperature and duration of thepre-cure will vary according to the physical properties of theparticular elastomeric material and according to the desired height H₁of the menisci 32 (see FIG. 4).

After passing through the oven or by the heaters, the housing and bobbinare positioned (230) in the elastomeric layer. In an alternativeexample, the housing and bobbin may be positioned while the elastomericlayer and release liner are at the elevated pre-cure temperature.

After placement of the housing and bobbin is completed, heat is appliedto increase (240) the temperature of the elastomeric layer to atemperature substantially greater than T₂ to fully cure the elastomericlayer. The duration of the cure is significantly longer than theduration of the pre-cure. The duration of the cure can be several hoursor more (e.g., a cure temperature of 150° C. for a four hour duration).

In some manufacturing environments, the pre-cure is performed in aseparate thermal environment from the cure operation. More specifically,the pre-cure may be performed using a process line oven or one or moreheaters, and the cure may be performed using a separate oven or heaterconfiguration. In this manner, the longer duration of the cure does notlimit the part throughput of the process line and the cure oven is usedas a separate batch process.

FIG. 7 shows a flowchart representation of an example of a method 300 offabricating a device having a compliant member in which the fabricationutilizes a UV pre-cure and UV cure. Reference is also made to FIG. 8which shows viscosity as a function of both irradiance and duration ofUV exposure for a UV-curable elastomeric material (UV Electro 225 (UVcuring Silopren™ liquid silicone rubber) available from MOMENTIVE™ ofWestford, N.Y.). The figure shows the storage modulus as a function ofUV irradiance duration for irradiances of 2 mW/cm2, 6 mW/cm2, 21.5mW/cm2 and 44.6 mW/cm2 (plots 50, 52, 54 and 56, respectively) using aUVA light source with a spectral output centered at approximately 365nm. There is an initial three second delay evident in each of the fourplots before UV irradiation was initiated. The differences in theinitial viscosities are attributable to variation in the sampletemperatures.

FIG. 8 demonstrates how a greater UV irradiance enables a full cure tobe achieved with shorter exposure duration. Similarly, the duration forthe pre-cure is less for a greater irradiance. The change in viscosityfrom uncured to fully-cured can be less than 100 times to more than1,000 times the viscosity of the uncured material.

According to the method 300, an elastomeric layer is provided (310) inan uncured state. The layer is irradiated (320) with UV light for apre-cure duration which, for example, can be less than 10 seconds toseveral minutes or more, and is dependent on irradiance. By way ofspecific examples, the UV light may be emitted from an arc lamp (e.g., amercury lamp) or one or more UV light emitting diode (LEDs). The UVirradiation of the elastomeric layer during pre-cure increases theviscosity of the layer to a level at which the layer is more resistantto flow. A lower irradiance requires a longer pre-cure duration;however, any variation in the increase in viscosity during the pre-curedue to differences in pre-cure durations for different fabrication runsis reduced. The preferred irradiance and duration for the UV pre-cure isbased on the particular material used and the desired meniscus geometry(see FIG. 4) to sufficiently reduce thickness variations in theelastomeric layer.

After completing the pre-cure, the housing and bobbin are positioned(330) so that their ends extend into the elastomeric layer. Although theelastomeric material migrates after the placement of the housing andbobbin, the increased viscosity limits the size of the menisci formedalong the housing and bobbin walls and, consequently, the thicknessvariations of the material are decreased relative to what otherwisewould occur for placement in an uncured material. Subsequently, theelastomeric layer is irradiated (340) with UV light to achieve a fullcure. The irradiance for the duration of the cure may be greater thanthe irradiance for the duration of the pre-cure. In addition, theduration of the cure may be substantially longer than the duration ofthe pre-cure and may be determined in part by the cure irradiance.Preferably, the UV source is configured with respect to the device sothat the elastomeric layer is not shadowed by the housing or bobbin forspatial consistency of the curing process; however, a dual cure materialthat can be cured by UV radiation and/or the application of heat may beused to avoid problems associated with shadow zones.

The UV pre-cure and UV cure processes may be separately completed. Forexample, the two processes may utilize different UV light sources. Inanother example, the pre-cure UV light source may be on a process lineand the cure UV light source may be a separate source configured forbatch irradiation of large numbers of parts so that the process linethroughput is not affected.

A number of implementations have been described. Nevertheless, it willbe understood that the foregoing description is intended to illustrate,and not to limit, the scope of the inventive concepts which are definedby the scope of the claims. Other examples are within the scope of thefollowing claims.

What is claimed is:
 1. A method of fabricating a device having acompliant member, comprising: providing an elastomeric layer in anuncured state; pre-curing the elastomeric layer to increase a viscosityof the elastomeric layer; positioning one or more of a bobbin and ahousing each having an end such that the end of the one or more of abobbin and a housing extends at least partially into the elastomericlayer; and curing the elastomeric layer such that the elastomeric layeris secured to the one or more of the bobbin and the housing.
 2. Themethod of claim 1 wherein the pre-curing of the elastomeric layercomprises applying heat to the elastomeric layer to increase atemperature of the elastomeric layer to a first temperature.
 3. Themethod of claim 2 wherein the curing of the elastomeric layer comprisesapplying heat to the elastomeric layer to increase the temperature ofthe elastomeric layer to a second temperature that is greater than thefirst temperature.
 4. The method of claim 3 wherein the pre-curingoccurs for a first duration and the curing occurs for a second duration,and wherein the first duration is less than the second duration.
 5. Themethod of claim 1 wherein the pre-curing comprises irradiating theelastomeric layer with ultraviolet light for a first duration.
 6. Themethod of claim 5 wherein the curing comprises irradiating theelastomeric layer with ultraviolet light for a second duration andwherein the second duration is greater than the first duration.
 7. Themethod of claim 1 wherein the pre-curing of the elastomeric layercomprises irradiating the elastomeric layer with ultraviolet light at afirst irradiance and the curing of the elastomeric layer comprisesirradiating the elastomeric layer with ultraviolet light at a secondirradiance, and wherein the second irradiance is greater than the firstirradiance.
 8. The method of claim 1 wherein the pre-curing comprisesapplying heat to the elastomeric layer and irradiating the elastomericlayer with ultraviolet light.
 9. The method of claim 1 wherein thecuring of the elastomeric layer comprises applying heat to theelastomeric layer and irradiating the elastomeric layer with ultravioletlight.
 10. The method of claim 1 wherein the elastomeric layer issecured to the bobbin and the housing, the method further comprisingremoving a portion of the elastomeric layer that extends outside adiameter of the housing.
 11. The method of claim 1 wherein theelastomeric layer in an uncured state comprises liquid silicone rubber.12. The method of claim 1 wherein positioning one or more of a bobbinand a housing further comprises positioning the bobbin inside thehousing.
 13. A device comprising: a compliant member having asubstantially planar shape and formed of a single layer of a curedelastomeric material; and one or more of a bobbin and a housing eachhaving an end that extends at least partially into the compliant member,wherein the elastomeric material adheres to a portion of the housingand/or bobbin at the end of the housing and/or bobbin to form a meniscushaving a height defined along a wall of the housing and/or bobbin andwherein the height of the meniscus is less than a height of a meniscusformed along the wall of the housing and/or bobbin for an uncured stateof the elastomeric material.
 14. The device of claim 13 wherein thehousing is a tube having an opening at the end.
 15. The device of claim13 wherein the elastomeric material comprises a silicone rubber.
 16. Thedevice of claim 13 wherein the complaint member includes a meniscusformed at each of an inner wall surface of the housing and/or bobbin andan outer wall surface of the housing and/or bobbin.
 17. A microspeakerdevice comprising: an acoustic diaphragm having a substantially planarshape and formed of a single layer of a cured elastomeric material; ahousing having an end extending at least partially into the singlelayer, wherein the single layer adheres to a portion of the housing atthe end of the housing to form a first meniscus having a height definedalong a wall of the housing, wherein the height of the first meniscus isless than a height of a meniscus along the wall of the housing for anuncured state of the elastomeric material; a bobbin disposed inside thehousing and having a surface and an end extending at least partiallyinto the single layer, wherein the single layer adheres to a portion ofthe bobbin at the end of the bobbin to form a second meniscus having aheight defined along a wall of the bobbin, wherein the height of thesecond meniscus is less than a height of a meniscus along the wall ofthe bobbin for the uncured single layer of the elastomeric material; anda coil wound on the surface of the bobbin.
 18. The microspeaker deviceof claim 17 wherein the first meniscus comprises a first inner meniscushaving a height along an inner wall surface of the housing and a firstouter meniscus having a height along an outer wall surface of thehousing and wherein the second meniscus comprises a second innermeniscus having a height along an inner wall surface of the bobbin and asecond outer meniscus having a height along an outer wall surface of thebobbin.
 19. The microspeaker of claim 17 wherein the housing and thebobbin are formed of different materials.
 20. The microspeaker of claim17 wherein the height of the first meniscus is different from the heightof the second meniscus.